John Williamson wrote:

I just bought some (fairly cheap) IR stereo headphones.
They work ok, but with a very audible hiss even at very
low volume when there is no sound from the source (PC).
This could quickly get annoying. I wondered if anyone
could tell me, is it that I just have a poor quality
product or is this sort of noise somehow inherent in the
technology?
Thanks for any help.
You get what you pay for? I've got a pair of Philips
cheapies that use analogue modulation on IR, they're
sitting in the cupboard waiting to get thrown out, they
sound that bad. Just about useable for low fidelity
speech, IMO.

In theory, digital transmission using IR can be made as
clean as CD or DVD. In practice, it's not cheap or easy to
do it that way.

I wonder if gain is partly controlled by carrier amplitude,
to compensate for changes in IR signal strength as you move
about? That could explain why noise, from receiving circuit
and background, gets so much worse in the absence of a
signal.

Assuming the listener's head is itself not a noisy IR
source, then the the high noise when the receptors are
blocked must come from the combination of a noisy receiving
circuit and high gain.

Perhaps it might be worth trying to return them for a
refund?

Ian